1. Field of Invention
The present invention relates to a variable valve lift apparatus. More particularly, the present invention relates to a multiple variable valve lift apparatus which is adapted to realize a plurality of valve lift modes.
2. Description of Related Art
Generally, an internal combustion engine generates power by combusting fuel and air supplied to a combustion chamber. Herein, an intake valve is operated by drive of a camshaft, and air flows into the combustion chamber during when the intake valve is open. In addition, an exhaust valve is operated by drive of a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Meanwhile, optimal operations of the intake valve or the exhaust valve are determined according to rotation speed of the engine. That is, lift and open/close timing of the valves are properly controlled according to rotation speed of the engine. A variable valve lift (VVL) apparatus has been developed in which a plurality of cams for operating the valves are provided to the camshaft or the valves are operated for various lifts according to rotation speed of the engine for realizing optimal operations of the valves according to rotation speed of the engine.
When the plurality of cams are provided to the camshaft, however, the composition for selectively changing the cam to operate the intake valve or the exhaust valve may become complex, and interference between the elements of the composition may occur.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.